Semiconductor components must be properly isolated from one another to function properly. For example, the state and conductance of individual transistors can only be controlled if proper isolation exists among the transistors. If not, leakage currents may occur, causing power dissipation, noise-margin degradation, and voltage shift on dynamic nodes. Additionally, cross talk among transistors can destroy the logic state of a gate.
In the past, field oxide bumps (LOCOS) have been used to isolate components of an integrated circuit. Field oxide bumps are typically formed by first pattern and etching the isolation areas. The substrate is then subjected to thermal treatment to grow field oxide at the isolation areas. Field oxide bumps are not scalable below 0.5 microns. Accordingly, field oxide bumps do not provide a satisfactory isolation system for sub 0.5 micron applications.
More recently, shallow trench isolation structures have been used for sub 0.5 micron applications. Typically, a narrow trench is formed in a substrate. The trench may be filled with an insulating material using high density plasma deposition to prevent voids from forming in the insulating material of the trench. High density plasma deposition results in a high density oxide that advantageously resists etching and other processing steps associated with semiconductor fabrication. Such shallow trench isolation structures, however, often leak current, which degrades integrated circuit performance.